Phenomenological Model for Prediction of Complex Ablation Geometries in Metal Films using Ultrashort Laser Pulses

Ablation of thin metal films with laser pulses having a pulse duration shorter than the electron-phonon relaxation time, so called ultrashort laser pulses, enables melt-free patterning of arbitrary geometries. Ablation with ultrashort laser pulses is an emerging process and is currently used in the field of microelectronics for the repair of photolithography masks and in the photovoltaic industry for patterning of ITO or for edge isolation. Another current field of investigation is the patterning of thin film strain sensors. In order to achieve the desired ablation quality, a multi-pulse irradiation is often required. Currently, there is no 'simple' model to predict predict line and more complex ablation geometries created by multi-pulse irradiation. Within this paper an incubation threshold is introduced to enhance an existing incubation model, which is restricted to the prediction of point ablations. The resulting phenomenological model is experimentally verified on thin NiCr films using 10 ps laser pulses. The usability of the derived model is significantly higher than other existing models due to concentrating on the relevant criterion for patterning of electronic circuits: the removal threshold as well as an easy to handle procedure to determine the model parameters, which can be determined on a machining setup in industrial conditions.

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